In recent years, as treatment for myocardial infarction or angina, coronary interventional procedure using a stent has been mainly performed.
However, since SUS316L or CoCr alloy used for the stent contains nickel ions in general, when the stent is used in the human body, nickel ions are eluted from the materials, and this is pointed out as the cause of restenosis (NPL 1).
Therefore, in order to suppress restenosis accompanied by implantation of a bare-metal stent, a Drug Eluting Stent (DES) containing a drug has been developed. However, the drug eluting stent has a problem that it exhibits a poor endothelialization ability after being implanted.
As a material used for stents, nickel-free high-nitrogen stainless steel (hereinafter, called HNS) has been developed. PTL 2 discloses that HNS can be prepared by electroslag remelting under N2 gas pressure (P-ESR). However, a stent formed of HNS also has a problem that it exhibits a poor endothelialization ability after being implanted.
If cytokine as a molecule that transmits signals to a cell is immobilized onto the surface of a metal, it may be possible to develop a stent having an excellent endothelialization ability without causing the elution of nickel ions. The cytokine includes, for example, Vascular Endothelial Growth Factor (VEGF). PTL 1 relates to effects of immobilized VEGF, and discloses that if VEGF is immobilized onto an artificial blood vessel together with fibronectin, growth of vascular endothelial cells is promoted, and movement speed of the cells increases. Moreover, NPL 3 relates to a cytokine-fixing method, and discloses that cytokine can be immobilized by dopamine treatment performed on the metal surface or a technique using a binding peptide searched by evolutionary molecular engineering.
However, when VEGF is chemically or physically bonded to the surface of a stent formed of HNS by the above-mentioned methods, the binding force becomes too strong, and accordingly, endothelial cells are likely to grow excessively.